Multiple magnetically tuned oscillator

ABSTRACT

YIG oscillator apparatus comprises both an FET-based YIG oscillator circuit and a bipolar transistor-based YIG oscillator circuit inside a single magnetic structure. Both YIG spheres are disposed in the single air gap of the magnetic structure, which is defined by a pole piece which is tapered to an elongated pole surface which is only slightly larger than necessary to cover both YIG spheres. A band reject filter is included inside the housing for rejecting second harmonics of desired oscillation frequencies only.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 07/725,388, filed Jun. 28, 1991, now U.S. Pat. No. 5,115,209,which is a continuation of U.S. patent application Ser. No. 07/592,859,filed Oct. 4, 1990, now abandoned. The immediate parent application isowned commonly with the present application and is incorporated hereinby reference in its entirety.

BACKGROUND

1. Field of the Invention

The invention relates to magnetically tuned resonant circuits.

2. Description of Related Art

A magnetically tuned resonator is a magnetic insulator which resonatesat a microwave frequency when placed in a magnetic field. If theresonator is spherical, the frequency of resonance is related only tothe strength of the magnetic field and not to the radius of the sphere.Magnetically tuned resonators in the spherical form usually have aradius between 0.5 mm and 1.0 mm, and in the most common case are madeof either single-crystal yttrium iron garnet or gallium-substitutedyttrium iron garnet. A number of other magnetic materials may also beused. All of these materials are referred to herein as YIG. Generalbackground material on YIGs and YIG circuits can be found in J.Helszajn, "YIG Resonators and Filters," John Wiley & Sons (New York:1985), incorporated by reference herein.

YIG resonators are used in several different types of microwavecircuits, including filters, limiters and oscillators. The presentinvention, while usable with certain other types of microwave circuits,is useful primarily in tuned oscillator circuits.

In a generalized oscillator circuit, a reactive component is coupled toan active device which incorporates feedback. Feedback may be eitherseries or parallel. For example, if the active device is an FET, thencommon source, common gate, and common drain configurations arepossible, all of which may incorporate either series or parallelfeedback. These configurations are shown at page 193 of Helszajn. In aYIG oscillator, a YIG sphere is used as a reactive component, and it isplaced in a magnetic field to set its resonant frequency. As usedherein, a reactive component need not be purely reactive; it can includesome resistance as well.

For a tunable YIG oscillator, the YIG sphere is placed in the air gap ofan electromagnet, and the current applied to the windings is varied asdesired in order to obtain the desired frequency of oscillation. Theelectromagnet usually has a re-entrant cylindrical shape comprising aclosed cylindrical magnetic shell having a pole piece extending inwardlyfrom one end. A second pole piece may extend inwardly from the oppositeend of the shell toward the first pole piece, but this is not essential.The end of the first pole piece defines a first pole surface, and theend of the second pole piece (or if there is no second pole piece thenthe other end of the magnetic shell itself) constitutes a second polesurface. The winding for the electromagnet is wrapped around at leastone of the pole pieces. The first pole surface has a circular shape witha radius slightly larger than that of the YIG sphere, in order to ensurethat the sphere is magnetized by a uniform magnetic field. The two polesurfaces are oriented parallel to each other for the same reason. Thepole piece is usually cylindrical in shape, and tapers near its end tothe size of the circular pole surface.

In the past, YIG oscillators have employed either an FET or a bipolartransistor as the active device coupled to the YIG resonator. FETs canoperate to much higher frequencies than bipolar transistors can, butbipolar transistors have significantly better noise characteristics.Thus, if a designer needed a YIG oscillator tunable within a lowerfrequency range, for example 2-8 GHz, a bipolar transistor-basedoscillator would be chosen. But if an oscillator tunable within a higherfrequency range, for example 8-20 GHz, was desired, an FET-basedoscillator would be chosen instead. No single broadband device has beenavailable which can be tuned to frequencies with both the bipolar andFET microwave frequency ranges. Attempts have been made to increase thehigh frequency limit of bipolar transistor-based YIG oscillators byincreasing the high frequency limit of the transistors, but thesetransistors have also tended to have higher minimum frequencies ofoperation. See, for example, Leung et al, "A 0.5 μm Silicon BipolarTransistor for Low-Phase Noise Oscillator Applications Up to 20 GHz,"1985 IEEE MTT-S Digest, pp. 383-386, and Leung et al, "Downsized BipolarFires 20 GHz Oscillator," Microwaves & RF (September 1985), pp. 163-168.Similarly, though FET-based YIG oscillator circuits can be designed tooperate at either low or high frequencies, it is difficult to design asingle circuit which can be tuned over the entire broadband. Thus, thereis a need for broadband tuned YIG oscillators in a single device.

According to the parent application, a broadband YIG tuned oscillatormay be obtained by combining two YIG oscillator circuits in a singlehousing with both YIG spheres being disposed in the same magneticstructure. The first circuit may be an FET-based oscillator circuitwhile the second circuit is a bipolar transistor-based oscillatorcircuit. The outputs of the two circuits are switchably coupled to anoutput terminal to enable the user to select the output of the bipolartransistor-based oscillator for lower frequencies and the output of theFET-based oscillator for higher frequencies. The current applied to thecoil for the sole electromagnet determines the frequency output of bothoscillator circuits.

While this arrangement works quite well, in certain implementations itmay be necessary to operate one of the oscillators at an operatingfrequency close to an edge of its optimum range. This could generatesome harmonic distortion when operated at that frequency which mayexceed desired specifications. For example, the bipolar oscillator maybe designed to operate within the range of 2-8.4 GHz, and the FEToscillator designed to operate within the range of 8.4-20 GHz. As theoperating frequency of the FET oscillator is reduced toward its lowerextreme, however, harmonic distortion tends to increase and may exceedthe desired specification.

One possible solution to this problem might be to design the FEToscillator to operate with a larger frequency range. This may bedifficult, especially if the oscillator must maintain its power outputand frequency range even at higher temperatures. Both power output andmaximum frequency tend to decrease as the temperature of an FET YIGoscillator increases.

Another solution might be to add a low-pass filter in the circuitryoutside the multiple YIG oscillator shell. However, such filterstypically are larger and have better performance specifications thantruly necessary to reduce the small excess in harmonic distortion.

SUMMARY OF THE INVENTION

It is therefore the object of the present invention to provide abroadband YIG tuned oscillator which can filter the second harmoniccomponent of an operating frequency without the need for extensiveexternal circuitry.

According to the invention, roughly stated, a simple band reject filteris inserted in the output of a dual YIG oscillator to filter the signalprovided by the selected one of the oscillators, before it reaches theoutput terminal of the unit. The band reject filter is designed toreject only those harmonic frequencies whose amplitude exceedsspecification (possibly in addition to integer multiples thereof). Thefilter may include a bias node coupled to a bias terminal accessibleexternally from the housing, so that the external circuitry mayselectively apply a bias and thereby activate the filter only whendesired, e.g. only when the external circuitry is operating theFET-based oscillator and doing so at the low end of its frequency range.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with respect to particular embodimentsthereof, and reference will be made to the drawings, in which:

FIG. 1 is a schematic diagram of a dual YIG oscillator circuit;

FIG. 2A is a top view of an electromagnet for use with the invention;

FIG. 2B is a cross sectional view of the electromagnet of FIG. 2A, takenalong lines B--B;

FIG. 2C is a cross sectional view of the electromagnet of FIG. 2A, takenalong either lines C--C or C'--C';

FIG. 3 is a layout diagram of portions of the circuit of FIG. 1; and

FIG. 4 is an enlarged view of the pole surface of the electromagnet ofFIG. 2;

FIGS. 5 and 6 are circuit diagrams of apparatus incorporating theinvention;

FIG. 7 is a layout diagram of the circuitry of FIG. 5.

DETAILED DESCRIPTION

A broadband dual YIG oscillator device is shown in circuit schematic inFIG. 1. It comprises a first, FET-based, YIG oscillator circuit 10, inwhich a YIG sphere 12 is coupled between ground and the gate terminal ofan FET 14. The source of the FET 14 is connected through a feedbacknetwork 16 to ground, and the drain of FET 14 is connected through abias and matching network 18 to a first positive terminal 20 and toground. An output 22 of the bias and matching network 18 forms theoutput of the oscillator circuit 10. Though the drain and source of FET14 are shown specifically in FIG. 1, it will be understood that becauseof the equivalence between these two terminals of an FET, the twoterminals may be interchanged for certain circuits. Both the drain andthe source terminals of an FET are referred to herein as "current pathterminals."

The feedback network 16 comprises a capacitor 30 coupled between thesource of FET 14 and ground. The source is also connected to oneterminal of an inductor 32, the other terminal of which is connected aparallel combination of a capacitor 34 and a resistor 36, both of whichare connected to ground.

The bias and matching network 18 includes a capacitor 40 coupled betweenthe drain of the FET 14 and ground. The drain of FET 14 is alsoconnected to one terminal of an inductor 42, the other terminal of whichis connected through a capacitor 44 to ground and a resistor 46 to thepositive supply terminal 20. The drain of FET 14 is also connectedthrough the series combination of a capacitor 48 and the resistor 50 toa node 52. The node 52 is connected through a resistor 54 to ground andthrough the series combination of a resistor 56 and a capacitor 58 tothe oscillator circuit output 22. The oscillator circuit output 22 isalso connected through the series combination of an inductor 60 and aresistor 62 to the positive supply terminal 20. A capacitor 61 couplesthe junction between inductor 60 and resistor 62 to ground.

The apparatus of FIG. 1 also includes a bipolar transistor-based YIGoscillator 110, comprising a YIG sphere 112 coupled between the emitterof a bipolar transistor 114 and a node which is coupled through acapacitor 116 to ground and through a resistor 118 to a negative supplyterminal 119. The base of transistor 114 is coupled through a feedbacknetwork 120 to ground, and the collector of transistor 114 is coupledthrough a bias and matching network 122 to a second positive supplyvoltage terminal 124 and to ground. An output 126 of the bias andmatching network 122 also forms the output of the oscillator circuit110.

The feedback network 120 comprises an inductor 130 coupled between thebase of transistor 114 and ground, and the series combination of aresistor 132, an inductor 134, and a capacitor 136 also coupled betweenthe base of transistor 114 and ground. The bias and matching network 122includes the series combination of an inductor 150 and a resistor 152coupled between the collector of transistor 114 and the positive supplyterminal 124. A capacitor 154 is coupled between ground and the junctionbetween inductor 150 and resistor 152. Inductor 150 is a tappedinductor, and the tap is connected through the series combination of aresistor 156, an inductor 158 and a capacitor 160 to ground.

The collector of transistor 114 is also coupled through a seriescapacitor 162 to a node 164, which is coupled through a capacitor 166 toground. The node 164 is coupled through a resistor 168 to a node 170,which is coupled through a resistor 172 to ground. The node 170 iscoupled through the series combination of a resistor 174 and a capacitor176 to the output 126 of the oscillator 110. The output 126 of theoscillator 110 is also coupled through an inductor 178 and resistor 180to the positive supply terminal 124, and the junction between inductor178 and resistor 180 is coupled through a capacitor 182 to ground.

Both the FET 14 and the bipolar transistor 114 should be operable withinmicrowave frequencies and should exhibit low noise. It will be seen,however, that neither needs to have optimum characteristics over a verylarge bandwidth. An example of a satisfactory FET is the JS8818 made byToshiba, and an example of a satisfactory bipolar transistor 114 is No.567 made by NEC.

The output 22 of the FET-based YIG oscillator circuit 10 is coupled tothe anode of a PIN diode 150, the cathode of which is connected to anode 152. Similarly, the output 126 of the bipolar transistor-based YIGoscillator circuit 110 is connected to the anode of a diode 154, thecathode of which is connected to the node 152. The node 152 is coupledthrough an inductor 156 to ground, and forms an AC-coupled input to anMMIC amplifier 160 through capacitor 153. The output of the amplifier160 is the output of the apparatus of FIG. 1.

The operation of each one of the oscillator circuits 10 and 110 isconventional and will not be described in detail here. It should benoted, however, that the bias and feedback arrangement 18 is such as tointroduce a positive DC component on the output line 22 so as to preventthe minimum voltage of the signal from falling below the thresholdvoltage of diode 150. Thus, as long as power is applied to the positivesupply terminal 20 and the YIG resonator 12 is oscillating, theoscillations generated by the oscillator circuit will reach the node152.

Similarly, the bias and matching network 122 in the oscillator circuit110 introduces an appropriate positive DC component to ensure that aslong as a positive supply voltage is applied to the terminal 124 and theYIG resonator 112 is oscillating, the oscillating signal from circuit110 will reach the node 152.

It should also be noted that the positive supply terminals 20 and 124are separate and distinct, meaning that a positive supply voltage can beapplied to one and not the other. In practice, a positive supply voltageshould be applied to only one of these terminals at a time, in order toselect which oscillator circuit will generate the signal which will beprovided to the amplifier 160. The diode 150 or 154 coupling the unusedoscillator circuit to node 152 will be reverse biased, therebyminimizing any effect which the unused oscillator circuit has on theoutput signal.

The circuitry of FIG. 1 is all supported by single printed circuit boardlocated inside an electromagnet which is shown in FIGS. 2A-2C. FIG. 2Ashows a top view of the electromagnet, with the top cover removed. FIG.2B shows a cross-section of the electromagnet, taken along lines B--B ofFIG. 2A. FIG. 2C shows another cross-sectional view of the structure,taken along either lines C--C or C'--C' of FIG. 2A. The cylindricalshell of the electromagnet structure is omitted from FIG. 2C forclarity.

Referring to all of the FIGS. 2A-2C, the electromagnet comprises acylindrical shell 200 which is closed on the bottom end by a bottomportion 202 and on the top end by a removable top cover 204. A polepiece 210 extends inwardly from the bottom portion 202. It iscylindrical in shape and includes a pole tip 212 which tapers to a polesurface 214. The pole surface 214 lies in a plane parallel to the topcover 204, and has an elongated shape for reasons which will becomeapparent below. The entire structure, including the cylindrical shell200, the two ends 202 and 204, and the pole piece 210, is made of aferromagnetic material such as Carpenter 49 and forms the core of theelectromagnet. A winding 216, shown symbolically in FIGS. 2B and 2C, iswrapped around the pole piece 210. Thus, when the winding 216 iscarrying current, the pole surface 214 and the inner surface 218 of thebottom cover constitute a pair of magnetically opposite poles. An airgap 220 exists between and is defined by these two poles. Epoxy 222,shown only in FIG. 2B, holds the coil in place.

A printed circuit board 230 is disposed inside the electromagnet and issupported by the cover 204 in such a way that a portion of the printedcircuit board is within the air gap 220.

FIG. 3 shows the layout of the circuit of FIG. 1, as supported on theprinted circuit board 230. The reverse side (not shown) of printedcircuit board 230, is plated with a ground plane. Referring to FIG. 3,in which components are numbered the same as in FIG. 1, the layout foreach respective one of the oscillators 10 and 110 is basicallyconventional. The FET transistor 14 is a chip bonded to a pad 402 on theprinted circuit board. The gate terminal of the FET 14 is connected viaa gold wire 404 and a meander line 406 to one terminal of a gold ribbon408. The gold ribbon 408 loops over the YIG sphere 12 and connects atits other end to a pad 410 which feeds through and connects to theground plane on the reverse side of the board. The YIG sphere 12 is heldin place under the loop by a beryllium oxide rod (not shown).

The source terminals of FET 14 are coupled to the ground plane throughthe capacitor 30, which takes the form of four open-circuitedtransmission lines. The source terminals of the FET 14 are also coupledthrough the inductor 32 to the top surface of the chip capacitor 34. Thebottom surface, which constitutes the opposite terminal of the capacitor34, is bonded to a pad 412 which feeds through to the ground plane. Thetop surface of the chip capacitor 34 is also connected via a wire 414 toone end of the thin film resistor 36, the other end of which isconnected to the ground plane via the pad 412.

The remaining components in the oscillator 10 are represented on thelayout of FIG. 3 similarly to those already described, so theinterconnections set forth above with respect to FIG. 1 will not berepeated.

In oscillator circuit 110, the bipolar transistor 114 is a chip havingits bottom (collector) surface bonded to a pad 450. The base and emitterterminals of the transistor 114 are on the top surface of the chip. Theemitter terminal is connected via a gold wire to a pad 452, to which isbonded one end of another gold ribbon 454. The gold ribbon 454 forms aloop over the second YIG resonator 112, and connects at its other end tothe top surface of a capacitor 116, the bottom surface of which isconnected to the ground plane on the reverse side of the board. The topsurface of the capacitor 116 is also connected via a gold wire and thethin film resistor 118 to the negative voltage terminal 119. As with thesphere 12 in the first oscillator circuit, this sphere 112 in the secondoscillator circuit is held in place by a beryllium oxide rod (notshown).

The base terminal of bipolar chip transistor 114 is connected by a goldwire to one end of the inductor 130, the other end of which is connectedby a gold wire to a pad 458 which feeds through to the ground plane. Thebase of bipolar chip transistor 114 is also connected to one side of athin film resistor 132, the other end of which connects via the inductor134 and capacitor 136 to the ground plane via the pad 458.

The collector terminal of bipolar chip transistor 114, which is bondedto the pad 450, is connected via another gold wire to a pad 460 on whichis bonded the chip capacitor 162. The top surface of the chip capacitor162 is connected by gold wires to capacitor 166, which is formed by aplurality of pads on the top surface of the printed circuit board incombination with the ground plane on the reverse side. Any number of thepads on the top surface can be connected together electrically in orderto appropriately tune the circuit. The pad 460 is also connected to thetapped inductor 150, the tap of which is connected via a thin filmresistor 156 to several structures which, in combination with the groundplane, provide the functions of both inductor 158 and capacitor 160.

As with the oscillator circuit 10, the remainder of the structures shownon the PC layout of FIG. 3 for oscillator circuit 110 correspond to, andare numbered identically with, the circuitry shown in FIG. 1, and,therefore, will not be further described here.

Though the two YIG spheres, 12 and 112, appear separated by asubstantial distance in FIG. 3, the scale is such that the two spheresare actually disposed near each other on the printed circuit board. Thisplaces them both within the same air gap 220 shown in FIG. 2B. Theprinted circuit board 230 is positioned within the electromagnet suchthat a projection of the two spheres onto the pole surface 214 liesentirely within the elongated area of the pole surface 214. The polesurface 214 should be longer in its major axis than the distance betweenthe opposite extremes of the two spheres as disposed on the board, andshould be wider in its minor axis than the diameter of the larger of thetwo spheres. The dimensions of the pole surface 214 should be onlyslightly larger than necessary to cover both spheres, however. Thispermits the device to operate at higher frequencies without saturating,since the saturation frequency increases with decreasing volume of theair gap 220. Minimizing the area of pole tip 214 is one way ofminimizing the volume of the air gap 220. It is for this reason that thepole tip 214 is not shaped simply as a circle large enough to encompassboth spheres, which would be much easier to machine. The size andelongated shape of the pole surface 214 shown in FIG. 2A represents aunique way of achieving an optimum compromise between the desire tofully encompass both spheres, to ensure a uniform magnetic field throughthem; the desire to minimize the pole surface area necessary to fullyencompass the spheres; and simplicity of manufacture.

The positive voltage supply terminals 20 and 124, the negative voltagesupply terminal 119, the ground terminal and the oscillator output 162,all pass through holes (not shown) in the cover 204 of the electromagnetand are available externally. The terminals of the coil 216 also passthrough holes (not shown) in the cover 204 and are accessibleexternally. Further, FIG. 4 shows an enlarged view of the pole surface214 of FIGS. 2A-2C. An auxiliary coil 300 is placed around thecircumference of the pole surface, the two terminals of which also passthrough holes (not shown) in the cover 204 of the electromagnet. Theauxiliary coil 300 is useful for fine tuning or frequency modulation ofthe output signal.

The two oscillator circuits 10 and 110 are chosen because, as previouslymentioned, it is desirable to use an FET-based circuit for higherfrequencies and a bipolar-based circuit for lower frequencies. Thus theoscillator circuit 10 is designed to output a signal with a frequencywhich varies substantially linearly with the strength of the magneticfield containing the YIG sphere 12, in the frequency range of 8-20 GHz,whereas the oscillator circuit 110 is designed to output a signal havinga frequency which varies substantially linearly with the strength of themagnetic field in the air gap 220 within the frequency range of about 2to 8 GHz. There is an overlap of a few hundred MHz in the two frequencyranges to allow a tolerance for component variations. Thus, an externalcircuit can obtain any frequency in the broadband of 2-20 GHz desired,simply by applying power to the positive supply terminal 20 or 124 ofwhichever oscillator circuit better produces that frequency, andapplying an appropriate current to the terminals of the coil winding216. This is accomplished in a single electromagnetic structure, nolarger than the more narrow band electromagnetic structures of the priorart, and using circuit components which do not need to push the state ofthe art in order to maximize their bandwidth.

Preferably, the external circuit has previously followed a calibrationprocedure and set up a table which specifies both the current to beapplied to the winding terminals and which oscillator circuit to power,for each desired output frequency.

FIG. 5 is a circuit drawing showing a modification to the circuit ofFIG. 1 to add a band reject filter. The output of the amplifier 160,instead of being connected directly to apparatus output 162, is insteadcoupled through a DC-blocking capacitor 402, a common filter node 404,and another DC blocking capacitor 403 to apparatus output 162. Thecommon node 404 is connected through a diode 406 to a shorted stub 408.The shorted stub 408 acts as a series tuned circuit having a resonantfrequency at about 18.4 GHz. As used herein, the diode 406 and shortedstub 408 constitute a filter element. An additional diode 410 and seriesconnected shorted stub 412 is also connected to the common node 404, andfurther filter elements such as these can be added as space permits.Each additional filter element connected to common node 404 increasesboth the depth and width of each notch in the band reject filter. Thecommon node 404 is also connected through an inductor 414 to a biasterminal 416, which is itself bypassed to ground by a capacitor 417. Thefilter components shown in FIG. 5 are all supported on the same printedcircuit board as the remainder of the YIG oscillator circuitry, insidethe shell, with the bias terminal 416 accessible from outside the shell.

In operation, when no bias voltage is applied to terminal 416, thesignal at the output of amplifier 160 is provided essentially unchangedto the apparatus output node 162. When a positive DC bias is applied tobias terminal 416, the filter is activated. The two-element filter shownin FIG. 5 attenuates frequencies within the range of about 16.8-20 GHz,which is the second harmonic of frequencies within the range of 8.4-10GHz, the low end of the FET oscillator operating range. It isadvantageous to activate the filter shown in FIG. 5 only when the FEToscillator is operating in the frequency range within which harmonicdistortion exceeds specifications, in order to minimize the effect whichthe circuitry has on normal operation of the device. For example, thefilter should not be active while the oscillator is being operated at afundamental between 16.8 and 20 GHz. Additionally, the filter shown inFIG. 5 includes a zero at 0 Hz, which could undesirably attenuate theoutput signal when the dual YIG oscillator is operated at lowfrequencies.

The filter of FIG. 5 includes two filter elements. This embodiment isuseful where board space is limited and the two shorted stubs 408 and412 must be disposed on opposite sides of the PC board tracecorresponding to node 404. If there is space for both shorted stubs onthe same side of 404, then one of the diodes such as 410 can beeliminated and the terminal of shorted stub 412 formerly connected todiode 410 can instead be connected to the junction between diode 406 andshorted stub 408. Additionally, a larger number of filter elements maybe used if desired, each additional element increasing both the widthand the depth of each notch in the band reject filter. The number offilter elements will be limited by board space and by any attenuationthat the widened zero response imposes on the pass band.

Advantageously, the amplifier 160 has a 50 ohm output impedance, and thefilter has both a 50 ohm input impedance and a 50 ohm output impedance.

Many variations are possible for the filter. FIG. 6 shows one variationin which the filter is inserted prior to the amplifier 160. Such anarrangement is not preferred since it forgoes the desirable isolationbetween the oscillators and the filter which the amplifier provides, butnevertheless is an option. In the circuit of FIG. 6, the output line 22of the FET oscillator 10 (FIG. 1) is connected, as shown in FIG. 1,through a diode 150 and a DC blocking capacitor 153 to the input ofamplifier 160, the output of which is provided to the apparatus outputnode 162. The oscillator output signal line 22 is also connected througha DC blocking capacitor 432 to a common filter node 434. A filterelement consisting of a diode 436 and a shorted stub 438 is connected tothe common filter node 434, as is an inductor 440 which couples the nodeto the external bias terminal 416. Similar considerations and variationsapply to the arrangement of FIG. 6 as are set forth above with respectto the arrangement of FIG. 5.

FIG. 7 is a board layout diagram showing the portion added to aconventional dual YIG oscillator corresponding to the addition of thefilter as shown in the circuitry diagram of FIG. 5. As with the layoutdiagram of FIG. 3, components shown in FIG. 7 which represent componentsalso shown in FIG. 5 are given the same numeric designation as they aregiven in FIG. 5. In particular, for example, the capacitor 153 has anunder surface connected to node 152 and a top surface connected viawires 502 to an input terminal 504 of the MMIC amplifier 160. Theamplifier 160 is mounted on a conductive plane 506, which is connectedthrough the PC board to the ground plane on the reverse side byfeed-through holes 507. The capacitor 402 is an integral part ofamplifier 160. The top surface of capacitor 402 is connected by wires510 to the common filter node 404, which is also the top surface ofcapacitor 403. The bottom surface of capacitor 403 is connected to theoutput node 162. The node 404 is connected via the inductor 414 to thetop surface of a capacitor 417, which is further connected to the biasterminal 416 (shown symbolically in FIG. 7). The underside of capacitor417 is connected to the plane 506.

Common filter node 404 is also connected through PIN diode 406 to thestub 408, the opposite end of which is connected through the PC board tothe ground plane on the reverse side as shown by circle 511. Similarly,the common filter node 404 is also connected through PIN diode 410 tostub 412, the opposite end of which is connected through to the groundplane on the reverse side of the PC board as shown by circle 512. Anadjustment strap 514 is also provided, connecting a point on the stub408 to the plane 506. By adjusting the placement of this strap 514 onthe stub 408, the resonant frequency of the stub 408 can be adjusted asrequired. A similar strap 516 is provided for the stub 412.

External circuitry (not shown) applies the DC bias voltage to the filterbias terminal 416 (FIGS. 5 and 7) only when the filtering characteristicis desired.

The invention has been described with respect to particular embodimentsthereof, and it will be understood that numerous modifications arepossible within its scope.

We claim:
 1. Magnetically tuned apparatus having an apparatus output,comprising:a first circuit including as a component a first magneticallytunable resonator, said first circuit outputting a first signal having afirst analog characteristic which varies as a first function of thestrength of the magnetic field containing said first resonator; a secondcircuit including as a component a second magnetically tunableresonator, said second circuit outputting a second signal having asecond analog characteristic which varies as a second function of thestrength of the magnetic field containing said second resonator;magnetic field generating means for generating a single magnetic field,said first and second resonators both being disposed in said singlemagnetic field; and switch means for providing to said apparatus outputan output signal responsive to selectably said first signal or saidsecond signal.
 2. Apparatus according to claim 1, wherein said first andsecond resonators are both spherical, wherein said first and secondcircuits are both oscillator circuits including said first and secondresonators as reactive components in respectively said first and secondoscillator circuits, and wherein said first and second analogcharacteristics are both frequency.
 3. Apparatus according to claim 2,wherein said first and second magnetically tunable resonators are bothYIG resonators.
 4. Magnetically tuned oscillator apparatus having anapparatus output, comprising:a first oscillator circuit having anoscillator output and including as a component a first magneticallytunable resonator, said first oscillator circuit outputting a firstoscillator signal having a frequency which is related to the strength ofthe magnetic field containing said first resonator by a first function;a second oscillator circuit having an oscillator output and including asa component a second magnetically tunable resonator, said secondoscillator circuit outputting a second oscillator signal having afrequency which is related to the strength of the magnetic fieldcontaining said second resonator by a second function; magnetic fieldgenerating means for generating a single magnetic field, said first andsecond resonators both being disposed in said single magnetic field; andswitch means for providing to said apparatus output an output signalresponsive to selectably said first oscillator signal or said secondoscillator signal.
 5. Apparatus according to claim 4, wherein said firstand second resonators are both spherical.
 6. Apparatus according toclaim 4, wherein said first and second magnetically tunable resonatorsare both YIG resonators.
 7. Apparatus according to claim 5, wherein saidfirst function is substantially linear over a first range of outputfrequencies and said second function is substantially linear over asecond range of output frequencies different from said first range ofoutput frequencies.
 8. Apparatus according to claim 7, wherein saidfirst range of output frequencies partially overlaps said second rangeof output frequencies.
 9. Apparatus according to claim 5, wherein saidfirst oscillator circuit further includes an FET as an active componentcoupled to said first resonator and said second oscillator circuitfurther includes a bipolar transistor as an active component coupled tosaid second resonator.
 10. Apparatus according to claim 5, wherein saidswitch means comprises:a first power supply terminal for applying powerto said first oscillator circuit; a second power supply terminal,distinct from said first power supply terminal, for applying power tosaid second oscillator circuit; and means for providing to saidapparatus output a signal responsive to both of said first and secondoscillator signals.
 11. Apparatus according to claim 10, wherein saidmeans for providing comprises:an amplifier having an amplifier input andan output being said apparatus output; a first diode coupling said firstoscillator output to said amplifier input; and a second diode couplingsaid second oscillator output to said amplifier input.
 12. Apparatusaccording to claim 5, wherein said magnetic field generating meanscomprises an electromagnet having a winding, said winding having firstand second terminals for applying a desired current thereto to controlthe strength of said single magnetic field.
 13. Magnetically tunedapparatus having an apparatus output node, said apparatus comprising:afirst oscillator circuit having first output and including a firstmagnetically tunable sphere as a reactive component and an FET as anactive component; a second oscillator circuit having a second output andincluding a second magnetically tunable sphere as a reactive componentand a bipolar transistor as an active component; an electromagnetincluding a pair of winding terminals for applying a desired currentthereto to control the strength of the magnetic field generated by saidelectromagnet, said first and second magnetically tunable spheres bothbeing disposed in said magnetic field; and switch means for outputtingselectably said first or second output on said apparatus output node.14. Apparatus according to claim 13, further comprising a first positivesupply terminal and a ground terminal, wherein said FET in said firstoscillator circuit includes a gate and first and second current pathterminals, and wherein said first oscillator circuit comprises:means forcoupling said gate of said FET to ground via said first magneticallytunable sphere; means for coupling said first current path terminal tosaid first positive supply terminal via an impedance; means for couplingsaid second current path terminal to ground; and means for coupling saidfirst current path terminal to said first output.
 15. Apparatusaccording to claim 13, further comprising a second positive supplyterminal, a ground terminal and a negative supply terminal, wherein saidbipolar transistor in said second oscillator circuit includes a base, acollector, and an emitter, and wherein said second oscillator circuitcomprises:means for coupling said emitter of said transistor to saidnegative supply terminal via said second magnetically tunable sphere;means for coupling said base of said transistor to ground; and means forcoupling said collector of said transistor to said second positivesupply terminal via an impedance, and for coupling said collector ofsaid transistor to said second output.
 16. Apparatus according to claim15, further comprising a first positive supply terminal, wherein saidFET in said first oscillator circuit includes a gate and first andsecond current path terminals, and wherein said first oscillator circuitcomprises:means for coupling said gate of said FET to ground via saidfirst magnetically tunable sphere; means for coupling said first currentpath terminal to said first positive supply terminal via an impedance;means for coupling said second current path terminal to ground; andmeans for coupling said first current path terminal to said firstoutput.
 17. Apparatus according to claim 16, wherein said first andsecond magnetically tunable spheres are both YIG spheres.
 18. Apparatusaccording to claim 16, wherein said switch means comprises:a first diodehaving an anode coupled to said first output and a cathode coupled tosaid apparatus output node; and a second diode having an anode coupledto said second output and a cathode coupled to said apparatus outputnode, said first and second positive supply terminals being distinct topermit application of power to selectably said first or secondoscillator circuits.
 19. Apparatus according to claim 13, wherein saidelectromagnet comprises:a magnetic core having first and secondmagnetically opposite pole surfaces, said core being shaped such thatsaid first and second pole surfaces face each other and define an airgap therebetween, said first pole surface lying in a plane substantiallyparallel to said second pole surface; a winding wrapping at least aportion of said magnetic core and electrically coupled between said pairof winding terminals; and support means for supporting said first andsecond magnetically tunable spheres in said air gap, at least said firstpole surface having an elongated shape which is slightly larger thannecessary to cover both said first and second magnetically tunablespheres as supported on said support means.
 20. Apparatus according toclaim 19, wherein said core forms a closed shell surrounding said airgap and includes a first pole piece extending inwardly to said air gapfrom said shell, said first pole surface being the free end of saidfirst pole piece, said first pole piece being substantially cylindricaland tapering to said elongated shape of said first pole surface. 21.Apparatus according to claim 20, wherein said support means comprises acircuit board, said first and second oscillator circuits also being onsaid circuit board inside said closed shell.
 22. Apparatus according toclaim 19, further comprising an auxiliary coil shaped as, and attachedto, the circumference of said first pole surface.
 23. YIG apparatushaving an apparatus output node, first and second positive supplyterminals, a negative supply terminal, a ground terminal and a pair ofwinding terminals, said apparatus comprising:a magnetic core forming aclosed shell and having a first pole piece extending inwardly from saidshell, the free end of said first pole piece constituting a first polesurface, said first pole piece being substantially cylindrical andtapering to the shape of said first pole surface, said core furtherhaving a second pole surface magnetically opposite said first polesurface, said first and second pole surfaces defining an air gaptherebetween; a winding wrapping at least a portion of said first polepiece and electrically coupled between said pair of winding terminals; acircuit board disposed inside said closed shell and supporting first andsecond oscillator circuits, said first oscillator having a first outputand said second oscillator circuit having a second output, said firstoscillator circuit including:a first YIG sphere, an FET having a gateand first and second current path terminals, means for coupling saidgate of said FET to ground via said first YIG sphere, means for couplingsaid first current path terminal to said first positive supply terminalvia an impedance, means for coupling said second current path terminalto ground, and means for coupling said first current path terminal tosaid first output; said second oscillator circuit including:a second YIGsphere, a bipolar transistor having a base, a collector and an emitter,means for coupling said emitter of said transistor to said negativesupply terminal via said second YIG sphere, means for coupling said baseof said transistor to ground, and means for coupling said collector ofsaid transistor to said second positive supply terminal via animpedance, and for coupling said collector of said transistor to saidsecond output; said first and second YIG spheres being disposedproximately on said circuit board and inside said air gap, at least saidfirst pole surface of said magnetic core having an elongated shape whichis slightly larger than necessary to cover both said first and secondspheres; said circuit board further supporting a first diode have ananode coupled to said first output and a cathode coupled to saidapparatus output node; and a second diode having an anode coupled tosaid second output and a cathode coupled to said apparatus output node,said first and second positive supply terminals being distinct to permitapplication of power to selectably said first or second oscillatorcircuits.
 24. Magnetically tuned apparatus having an apparatus output,comprising:a first circuit including as a component a first magneticallytunable resonator, said first circuit outputting a first signal having afirst analog characteristic which varies as a first function of thestrength of the magnetic field containing said first resonator; a secondcircuit including as a component a second magnetically tunableresonator, said second circuit outputting a second signal having asecond analog characteristic which varies as a second function of thestrength of the magnetic field containing said second resonator; aclosed shell; magnetic field generating means for generating a singlemagnetic field in said closed shell, said first and second resonatorsboth being disposed in said single magnetic field; switch means forproviding a switch output signal responsive to selectably said firstsignal or said second signal; and filter means for filtering said switchoutput signal to produce a filter output signal, and providing saidfilter output signal to said apparatus output, said filter means beingdisposed inside said closed shell.
 25. Apparatus according to claim 24,further comprising means for amplifying said switch output signal beforebeing filtered by said filter means.
 26. Apparatus according to claim24, further comprising means for amplifying said filter output signalbefore being provided to said apparatus output.
 27. Apparatus accordingto claim 24, wherein said first and second resonators are bothspherical, wherein said first and second circuits are both oscillatorcircuits including said first and second resonators as reactivecomponents in respectively said first and second oscillator circuits,and wherein said first and second analog characteristics are bothfrequency.
 28. Apparatus according to claim 24, wherein said first andsecond resonators are both YIG resonators.
 29. Magnetically tunedoscillator apparatus having an apparatus output, comprising:a firstoscillator circuit having an oscillator output and including as acomponent a first magnetically tunable resonator, said first oscillatorcircuit outputting a first oscillator signal having a frequency which isrelated to the strength of the magnetic field containing said firstresonator by a first function; a second oscillator circuit having anoscillator output and including as a component a second magneticallytunable resonator, said second oscillator circuit outputting a secondoscillator signal having a frequency which is related to the strength ofthe magnetic field containing said second resonator by a secondfunction; a closed shell; magnetic field generating means for generatinga single magnetic field, said first and second resonators both beingdisposed in said single magnetic field; switch means for providing aswitch output signal responsive to selectably said first oscillatorsignal or said second oscillator signal; and filter means for filteringsaid switch output signal to produce a filter output signal, andproviding said filter output signal to said apparatus output, saidfilter means being disposed inside said closed shell.
 30. Apparatusaccording to claim 29, further comprising means for amplifying saidswitch output signal before being filtered by said filter means. 31.Apparatus according to claim 29, further comprising means for amplifyingsaid filter output signal before being provided to said apparatusoutput.
 32. Apparatus according to claim 29, wherein said first andsecond resonators are both spherical.
 33. Apparatus according to claim32, wherein said first function is substantially linear over a firstrange of output frequencies and said second function is substantiallylinear over a second range of output frequencies different from saidfirst range of output frequencies.
 34. Appratus according to claim 33,wherein said first range of output frequencies partially overlaps saidsecond range of output frequencies.
 35. Apparatus according to claim 32,wherein said first oscillator circuit further includes an FET as anactive component coupled to said first resonator and said secondoscillator circuit further includes a bipolar transistor as an activecomponent coupled to said second resonator.
 36. Apparatus according toclaim 35, wherein said first and second resonators are both YIGresonators.
 37. Apparatus according to claim 32, wherein said switchmeans comprises:a first power supply terminal for applying power to saidfirst oscillator circuit; a second power supply terminal, distinct fromsaid first power supply terminal, for applying power to said secondoscillator circuit; and means for providing to said apparatus output asignal responsive to both of said first and second oscillator signals.38. Apparatus according to claim 37, wherein said means for providingcomprises:an amplifier having an amplifier input and an output beingsaid apparatus output; a first diode coupling said first oscillatoroutput to said amplifier input; and a second diode coupling said secondoscillator output to said amplifier input.
 39. Apparatus according toclaim 32, wherein said magnetic field generating means comprises anelectromagnet having a winding inside said shell, said winding havingfirst and second terminals for applying a desired current thereto tocontrol the strength of said single magnetic field.
 40. Apparatusaccording to claim 32, wherein one of said first and second oscillatorcircuits generates an undesirably large harmonic when operating at aparticular frequency, and wherein said filter means comprises bandreject means for reducing the magnitude of said harmonic.
 41. Apparatusaccording to claim 40, further comprising activating means foractivating said filter means when said one of said oscillator circuitsis operating at said particular frequency.
 42. Apparatus according toclaim 32, further comprising activating means for activating said filtermeans at desired times.
 43. Magnetically tuned apparatus having anapparatus output node, said apparatus comprising:a first oscillatorcircuit having a first output and including a first magnetically tunablesphere as a reactive component and an FET as an active component; asecond oscillator circuit having a second output and including a secondmagnetically tunable sphere as a reactive component and a bipolartransistor as an active component; a closed shell; an electromagnetincluding a pair of winding terminals for applying a desired currentthereto to control the strength of the magnetic field generated by saidelectromagnet, said magnetic field being generated inside said shell,said first and second magnetically tunable spheres both being disposedin said magnetic field; switch means for outputting selectably saidfirst or second output signal as a switch output signal; and filtermeans for filtering said switch output signal to produce a filter outputsignal, and providing said filter output signal to said apparatusoutput, said filter means being disposed inside said closed shell. 44.Apparatus according to claim 43, wherein said first and secondmagnetically tunable spheres are both YIG spheres.
 45. Apparatusaccording to claim 44, further comprising a first positive supplyterminal and a ground terminal, wherein said FET in said firstoscillator circuit includes a gate and first and second current pathterminals, and wherein said first oscillator circuit comprises:means forcoupling said gate of said FET to ground via said first magneticallytunable sphere; means for coupling said first current path terminal tosaid first positive supply terminal via an impedance; means for couplingsaid second current path terminal to ground; and means for coupling saidfirst current path terminal to said first output.
 46. Apparatusaccording to claim 44, further comprising a second positive supplyterminal, a ground terminal and a negative supply terminal, wherein saidbipolar transistor in said second oscillator circuit includes a base, acollector, and an emitter, and wherein said second oscillator circuitcomprises:means for coupling said emitter of said transistor to saidnegative supply terminal via said second magnetically tunable sphere;means for coupling said base of said transistor to ground; and means forcoupling said collector of said transistor to said second positivesupply terminal via an impedance, and for coupling said collector ofsaid transistor to said second output.
 47. Apparatus according to claim46, further comprising a first positive supply terminal, wherein saidFET in said first oscillator circuit includes a gate and first andsecond current path terminals, and wherein said first oscillator circuitcomprises:means for coupling said gate of said FET to ground via saidfirst magnetically tunable sphere; means for coupling said first currentpath terminal to said first positive supply terminal via an impedance;means for coupling said second current path terminal to ground; andmeans for coupling said first current path terminal to said firstoutput.
 48. Apparatus according to claim 47, wherein said switch meanscomprises:a first diode having an anode coupled to said first output anda cathode coupled to said apparatus output node; and a second diodehaving an anode coupled to said second output and a cathode coupled tosaid apparatus output node, said first and second positive supplyterminals being distinct to permit application of power to selectablysaid first or second oscillator circuits.
 49. Apparatus according toclaim 48, wherein said filter means comprises:a node, said filter meansbecoming operative only upon application of a bias voltage to said node;first D.C. blocking means for blocking D.C. transmission between saidswitch means and said node; second D.C. blocking means for blocking D.C.transmission between said node and said apparatus output; and a biasterminal coupled to said node, said bias terminal being accessible fromoutside said shell to permit application of a D.C. bias only at desiredtimes.
 50. Apparatus according to claim 44, wherein said filter meanscomprises:a node, said filter means becoming operative only uponapplication of a bias voltage to said node; first D.C. blocking meansfor blocking D.C. transmission between said switch means and said node;second D.C. blocking means for blocking D.C. transmission between saidnode and said apparatus output; and a bias terminal coupled to saidnode, said bias terminal being accessible from outside said shell topermit application of a D.C. bias only at desired times.
 51. YIGapparatus having an apparatus output node, a common node, first andsecond positive supply terminals, a negative supply terminal, a groundterminal, a filter bias terminal, and a pair of winding terminals, saidapparatus comprising:a magnetic core forming a closed shell and having afirst pole piece extending inwardly from said shell, the free end ofsaid first pole piece constituting a first pole surface, said first polepiece being substantially cylindrical and tapering to the shape of saidfirst pole surface, said core further having a second pole surfacemagnetically opposite said first pole surface, said first and secondpole surfaces defining an air gap therebetween; a winding wrapping atleast a portion of said first pole piece and electrically coupledbetween said pair of winding terminals; a circuit board disposed insidesaid closed shell and supporting first and second oscillator circuits,said first oscillator circuit having a first output and said secondoscillator circuit having a second output, said first oscillator circuitincluding:a first YIG sphere, an FET having a gate and first and secondcurrent path terminals, means for coupling said gate of said FET toground via said first YIG sphere, means for coupling said first currentpath terminal to said first positive supply terminal via an impedance,means for coupling said second current path terminal to ground, andmeans for coupling said first current path terminal to said firstoutput; said second oscillator circuit including:a second YIG sphere, abipolar transistor having a base, a collector and an emitter, means forcoupling said emitter of said transistor to said negative supplyterminal via said second YIG sphere, means for coupling said base ofsaid transistor to ground, and means for coupling said collector of saidtransistor to said second positive supply terminal via an impedance, andfor coupling said collector of said transistor to said second output;said first and second YIG spheres being disposed proximately on saidcircuit board and inside said air gap, at least said first pole surfaceof said magnetic core having an elongated shape which is larger thannecessary to cover both said first and second spheres; said circuitboard further supporting a first diode have an anode coupled to saidfirst output and a cathode coupled to said common node; a second diodehaving an anode coupled to said second output and a cathode coupled tosaid common node, said first and second positive supply terminals beingdistinct to permit application of power to selectably said first orsecond oscillator circuits; a band reject filter coupled between saidcommon node and said apparatus output node, said filter having a biasnode and operating only when a bias voltage is applied to said biasnode; and means for coupling said bias node to said bias terminal topermit application of said bias voltage only at desired times.